In general terms, with reference to the case of electronic power circuits used for piloting the solenoid valves of fuel injectors, the occurrence of a fault can be traced back to the appearance of one of the following phenomena:
the breaking of the connection to the injector solenoid valve, which acts as the load of the circuit (open load); PA0 the establishment of a short circuit to earth, or PA0 the establishment of a short circuit to the voltage supply (battery) of the load.
Moreover, if--as is usually the case--there are several power circuits operating in parallel (usually one for each injector) it is also important to be able to provide an indication which identifies the stage or stages where the fault has arisen.